Final answer:
Fuses and circuit breakers act as automatic switches that open when the sustained current exceeds desired limits in a parallel circuit, providing protection against overloading and potential hazards.
Step-by-step explanation:
When you add a fuse or circuit breaker to the main line of a parallel circuit, they act as automatic switches that open when the sustained current exceeds desired limits.For example, in a parallel circuit with multiple devices like an 1800-W toaster, a 1400-W speaker, and a 75-W lamp, each device will draw a different amount of current based on their power ratings. The fuse or circuit breaker will open (blow) if the total current drawn by these devices exceeds the desired limit, in this case, the 15-A fuse rating.Fuses and circuit breakers are essential for protecting the circuit from excessive current and preventing potential hazards, such as overloading and electrical fires.